Sustainability
is an ethical concept that things should always be better in the future than
they are at present. It is a commitment to continuous, monotonic
improvement in the human condition. That is, sustainability is not an
optimization or a maximization principle. It is about the direction, not
the pace. Thus, sustainability is about the compass, not the speedometer.

Continuous
improvement in the human condition requires that all humans have the
opportunity to improve their condition -- that includes rich and poor, present
and future. Thus, sustainability is not inherently egalitarian nor
hierarchical, except that it does admit that the rate of
improvement in some populations may be slowed so as to ensure that all segments
can improve.